Recording of alternating current impulses



F125. 3, 1942. E. w.- KELLOGG i 2,271,980

RECORDING OF ALTERNATING CURRENT IMPULKSES K Filed Nav. s, 1939@shwrs-sheet 1 Edward Wifellagg Feb.'3, 1.942. E, KELLQGG .2,271,980 l'RECORDING 0F ALTERNATING CURRENT IMPULSES Fild Nov. 8, 19:59 2sheets-sheet 2'.

' Imventot Edward Wllla Q vPatented Feb. 3, -1942 ULSES Edward W.Kellogg, Moorestown, N. assignor to Radio Corporation of America, acorporation of Delaware Application November 8, 1939, Serial No. 303,373

5 Claims. (Cl. 179-1003) invention relates to the recording ofalternating current impulses such as those of audio frequency, and hasfor its principal object thev provision of an improved recordingapparatus and method of operation for producing a class A `push-pullrecord having its diierent record f tracks registered in different orcomplementarycolors. -As is Well known, the recorded impulses arereproduced from such a record through the medium of color filters,prisms or the like.

A class A type of record is one wherein the positive and negativerecordareas are so disposed as to simultaneously aiect a pair ofpushpull connected photoelectric elements.v The positive and negativehalf cycle record areas, arranged to simultaneously affect the push-pullphotoelectric elements,may be on the same .or different record tracks,the selection of the half cycle record areas being effectedgeometrically, by color, by carrier frequency, by polarization or byother suitable means. l

Color separation, for example, involves the employment of tworeproducing elements, one of which is aected only by light of a certaincolor, and the other of which is affected only by light of anothercolor. The sound track includes differently stained areas which willrespectively absorb light of the two different colors. For example, thereproducing elements may be two photocells with two complementary colorfilters such as red' and blue in front of the rst and second cells,respectively, and the sound track may be recorded by the application ofred and blue dyes or stains, each of which absorbs light; of itscomplementary color, but comparatively little light of its own color.Thus the photocell having the red filter receives light which isstrongly modulated by the presence of blue dye in thesound track but isrelatively little alected by the presence of red dye in the sound track.

This invention is related to those disclosed by United States Patent2,102,695 of Giesking, by

` application Serial No. 196,554 .of Hullegard, and

by application Serial No. 287,324 of Dimmick, all assigned to the sameassignee as the present application. As will appear, all of theseinventions involve recording indifferent colors the positive andnegative half cycles of a sound wave or other alternating impulse. Onesuitable recording material for this purpose is the multi-color motionpicture nlm currently sold under the tradename Kodachrome, but if theonly color requirements are for the sound track, a simpler film havingonly two emulsion layers, instead of three as in the case of Kodachrome,would suilice, 55

and the processing of the two color film would be correspondinglysimpler.

The invention will be` better understood from the' following descriptionconsidered in connection with" the accompanying drawings, and its scopeis indicated by the appended claims.

Referring to the drawings: Figure 1 diagrammatically illustrates adevice suitable for recording alternating impulses in the form ofduplicate record tracks with their corresponding half cycles ofAdifferent colors,

Figure 2 illustrates certain details of the device'of Fig. 1,

Figure 3 illustrates the record produced by the device of Fig. 1, Figure4 illustrates a modification in certain details of the device of Fig. l,and

Figure 5 illustrates fthe record produced by the modified device.

Figure 6 illustrates an alternative method of obtaining ground noisereduction.

Figure 7 illustrates a sound lllm in which the unused areas are black.

The recording device of Fig. 1 includes alight source I0 from whichlight is projected through a" multi-colored mask II and lens I2 to'agalvanometer mirror I4, which is vibrated in accordance with theelectrical impulses transmitted through its operating coil I5. Light isreflected from the mirror I4 through. the lens I3, a light slit I'I andlenses I8 and I9 to a film 20 upon which the impulses are recorded.'I'he manner in which this recording system works to produce thephotographic record of the sound is well understood, being the same asin the case of the recording systems now in commercial use in makingvariable area records.v

From a light source 2I, light is projected through an apertured mask, aslit 22 and lenses 23 and 24 to the record strip 20, for exposing toAwhite light the record area not required for modulatingthe light beam ofthe reproducer.

This is in accordance with the well known principle employed in groundnoise reduction systems as applied to variable area photographic soundrecording. In order to restrict this exposure to areas not occupied bythe -record tracks, a V- shaped shutter 25 is arranged to be moved toand' fro transversely of the slit 22, in response to Variation in theramplitude or volume of the recorded impulses. To this end, the operatingcoil A26 of the shutter 25 issupplied with a direct current which variesin accordance with the volume of the recorded impulses. Suitable meansfor deriving such current are so well known as to require no descriptionhere. 'I'he recording device so far described is substantially the sameas that employed in the system for making direct positive, recordingsdescribed by G. L. Dimmick, copending U. S. application Serial No.287,324, filed July 29, 1939 (RCV D-6030), except that in the system ofDimmick an opaque mask having a triangular opening, instead of the twocomplementarily colored filters shown at I I in my Fig. 1.

As shown more clearly in Fig. 2, the recording slit I1 and the shadingor noise reduction slit 22 may be formed in the same mask 21; astationary light beam is projected on the slit 22 from the light source2|; the shutter 25 is vibrated transversely of the slit 22;v and themulti-colored light beam, or image 29 of the composite filter II, isvibrated transversely of the slit I1.

It will be noted the red and blue filter areas of the mask I I areseparated bya diagonal boundary line, that the multi-colored image 29contains similarly separated blue and red areas, and that the diagonalboundary line between the dif-A ferently colored image areas extendsobliquely across the impulse recording slit I1. Vibration of themulti-colored image transversely of the slit I1 therefore causes theboundary between the record areas exposed to the differently coloredparts of the beam to Vary transversely of the record in accordance withthe impulses to be recorded. As a result of this, assuming that the filmon which the record is being made is one wherein exposure to light of agiven color results in dyed image of -the same color, there is produceda record which diers from the usual black and White variable area orvariable width record only in that'the black and white areas arereplaced, respectively, by red and blue areas.

In order to minimize the background noise otherwise incident to theplaying of a photographic sound record, it is common practice to blackenthe areas of the sound track which lie outside the envelope of therecorded waves. This has no effect on the useful sound as reproduced,provided the boundary of the blackened area has only gradual curvatures,but black film gives rise to much less random ground noise than -anequal area of clear film; hence .as much area is blackened in thismanner as is compatible with avoidance of interference with therecording of the Waves. In a sound record of the type involved in thisinvention, wherein the light for operating two photocells in pushconnection, is separated by color filters, colorless film is almost asfree from noise as black film, on account of the neutralizing action ofthe push-pull circuit for disturbances which affect both photocellsequally. It is therefore almost as effective to make the unused areasclear as to make them black, the ground noise depending principally onthe total area of colored film within the area scanned by thereproducing system. The ground noise reduction system employed inconnection with a colored sound track system of the type illustratedherein may optionally consist in arrangements for making the unusedareas either clear and colorless or black- I have chosen to illustratethe embodiment of my invention wherein the unused areas are clear. Ifthe film on which the sound is recorded is of a type such as Kodachrome,wherein exposure to light of a given color, results in the xing of a dyeof the same color, the complementary colored dyes being dissolved out,exposure to white light in suiiicient amount results in clear iilm. Thusthe portions of the lm which receive white light exposure through theauxiliary slit 22 of Fig. 1 are clear, and this Iaccomplishes groundnoise reduction. The shutter25 is moved transversely of the slit 22 inaccordance with the volume of the recorded impulses, thus producing theclear areas indicated on the record illustrated in Fig. 3. This recordmay be played by any suitable type l of color separation reproducer,such Ias those disclosed by the aforesaid copending Dimmick application.

An alternative method of obtaining ground noise reduction is to @employa shutter which obscures part of the recording beam, as shown in Fig. 6,in which the plate 21 is provided with only one slit I1 through whichthe light for recording the sound passes. The lamp 2I and lenses 23-24are omitted. The filter II is imaged on the plate 21 as a red and bluelight spot 29 which vibrates up and down in response to sound vibrationsas in the case of the arrangement illustrated in Fig. 1. A shutter vane33 having a V-shaped notch 34 obstructs the light 29 so that it does notpass through the slit I1, except for a small region near the middle ofthe slit where the boundary between the red and blue areas intersectsthe slit. As the modulation increases, the shutter vane is moveddownward by a magnet corresponding to that shown at 26 in Fig. 1 anduncovers enough of the slit I1 to accommodate the modulation so that thevibratory movements of the light spot 29 never result in the exposedpart of the slit being illuminated entirely with light of one color. Atmodulation, the shutter vane is completely out of the way and the fulllength of the slit is illuminated. The resulting sound record, if thefilm is of the same type already discussed, will be like that shown inFig. 7, areas to the right and left of the modulation area being blackinstead of clear as in Fig. 3.

The form of apparatus shown in Figs. 1 and 2 has an advantage over thatof Fig. 6 in that the use of an extra slit and light source foreffecting the ground noise reduction permits a displacement of theposition at which the noise reduction exposure is applied and that atwhich the sound waves are recorded. When there is a quick increase inthe amplitude of the modulation, this displacementgives the shutter vanetime to move the requisite amount so that none of the wave outlines areobliterated. In the arrangement of Fig. 6, overmodulation occurs if theshutter fails to move out of the Way fast enough.

If the type of film and method of processing the same do not have to beadapted to producing a colored picture of the usual kind, as, forexample, when recording sound only, the apparatus of Fig. l may be usedand a method of processing may be followed which will produce a track ofthe type just described wherein the unused areas are black instead ofclear. The type of film represented by Kodachrome is what may be calleda color positive in that the exposures makes the film transparent. Themaking of a colored sound negative, using, for example, the recordingsystemv illustrated in Fig. 1, would be substantial` ly as follows.Since only two complementary colors are required, a double emulsion lmwill suflice.

Next the base would be a red-sensitive emulsion over which would be athin layer of stained gelatine constituting a yellow-orange or redfilter, and the outer layer would be an emulsion sensitive to blue lightonly. After exposure, the film would be developed without reversal, and

the :developedsilver imagesv in the two layers would` be transformedinto colored images by toning or iixing of appropriate dyes. This is awell known photographic process. The under layer 'may be toned red andthe outer layer toned blue, or vice versa, since the sound reproductionwill be equally satisfactory in either case.v Areas which have not beenexposed to light of either [color will come out clear, and areas exposedto? white light or both red and blue light will 'beblack. Thecolor-'deposited inthe two vlayers' may be determined by depending onthe vdierence in penetration in successive baths as is done while therecords of Figs. 3 and 5 are in lsome respects similar tol those of theaforesaid patent Aand patent application, "they differ therefromv inthat they include differentlycolored*areas separated by a commonboundary'line which varies transversely of the record in accordance withthe recorded. impulses. The outside-or noncommon .boundary lines ofthese diierently colored areas, of course,y vary in accordance with thevolume -of recorded impulses. -Modulation of the reproduced light isthus effected by dii'- fercntly colored areas whichare interlaced.contiguous, mutually exclusive and restricted to the in Kodachrome orbyincorporating in each layer, when the film is made, a suitable dye-cou-`pling agent which-will not dissolve outin the developing process, andwhich will take part in forming the appropriate stain. The lastmentioned'process isy employed in a tem of the Agfa Company. y

A sound film in which the unused areas are color film sysblack, las inFig. 7, has an advantage over one in which they are clear in that lowground noise is less dependent on balance between the two photocells andless impaired by lack o'f saturated colors in the film. A recommendedprocedure when a number of prints are needed is to use like Fig. 7, andto use this negative to print sound tracks o n the iinal or releaseprints, the pic-l tures being printed from a separate master colorpicture lm. The prints would then be processed with reversaldevelopment, as in the case of Kodachrome, to give a iinal iilm inwhichthe color 'is the same as that of the light to which the print iilmwas exposed. This mode of operating will be in accordance with thestandard` method of making color picture duplicates on Kodachrome orsimilar film, while the sound track will have the two-color sound waverecord, with the unused areas substantiallyopaque.

The modification of Fig. 4 differs from the preceding modification inthat (1) the maskll is replaced by a mask which produces a multi-co1-ored image wherein the boundary line between the differently coloredareas is V-shaped f and (2) the 'noise reduction shutter 25 is replacedby a W-shaped or multi-point shutter 3l. y

The record resulting from this modification is shown in Fig. 5. This isreadily recognized as a multi-track or bilateral push-pull record whichmay be played by any suitable push-pull reproducer of the colorseparation type.

. the apparatus of Fig. 1 to make a sound negative minimum area requiredfor modulation purposes. l5

I claim as my invention: I 1. AAn alternating current impulse recordincluding differently `colored Aareas separated by a common boundaryline which variestransversely of the record `in accordance with'therecorded impulses. 2. An alternating current impulse record includingdiiierently colored areas separated by -a' common boundary line whichvaries transversely .of the record in accordance with therecordedimpulses, and neutral areas which vary along the non-commonboundary lines of said differently colored areas in accordance with the'volume of said impulses. i

3. An alternating current impulse record in cluding dierently-coloredareas which are contiguous, mutually exclusive andl separated by acommon boundary line of a contour dependent on the waveshape of therecorded impulses.

accordance with said impulses, and means responsive to the volume vofsaid impulses for restricting the recording eiiect of said differentlycolored light beams 'to such record area as is required to permitmodulation of said impulses.

EDWARD w.

